Local oscillator with non-harmonic ratio between oscillator and RF frequencies using pulse generation and selection

ABSTRACT

A novel and useful apparatus for and method of local oscillator (LO) generation with non-integer multiplication ratio between the local oscillator and RF frequencies. The LO generation schemes presented are operative to generate I and Q square waves at a designated frequency while avoiding the well known issue of harmonic pulling. The input signal is fed to a synthesizer timed to a rational multiplier of the RF frequency L/N f RF . The clock signal generated is divided by a factor Q to form 2Q phases of the clock at a frequency of L(N*Q) f RF , wherein each phase undergoes division by L. The phase signals are input to a pulse generator which outputs a plurality of pulses. The pulses are input to a selector which selects which signal to output at any point in time. By controlling the selector, the output clock is generated as a TDM based signal. Any spurs are removed by an optional filter.

REFERENCE TO PRIORITY APPLICATION

This application claims priority to U.S. Provisional Application Ser.No. 60/823,837, filed Aug. 29, 2006, entitled “Generation ofLocal-Oscillator Signal with Non-Integer Multiplication Ratio Betweenthe Local-Oscillator and the RF Frequencies”, incorporated herein byreference in its entirety.

FIELD OF THE INVENTION

The present invention relates to the field of data communications andmore particularly relates to a local oscillator (LO) circuit withnon-integer multiplication ratio between the local oscillator and RFfrequencies.

BACKGROUND OF THE INVENTION

The use of local oscillator generation circuits for wirelesstransceivers is well known in the art. The local oscillator is generatedas a continuous wave (CW) and is then used for quadrature modulation ordemodulation of transmitted and received signals respectively.Alternatively, the oscillator can also perform frequency modulation aspart of a polar transmitter architecture system.

A block diagram illustrating an example prior art phase locked look(PLL)-based local oscillator (LO) generator circuit is shown in FIG. 1.The typical PLL LO generation circuit, generally referenced 10,comprises phase detector (PD) 14, loop filter or low pass filter (LPF)18, controlled oscillator 22, resonator 26 and frequency divider 28.

In operation, a reference signal 12, normally generated by a crystaloscillator, is input to the phase detector 14 along with a divided-downRF frequency continuous wave (CW) 29. The phase detector, typicallyimplemented as a charge pump or mixer, generates a phase error (PE orPHE) 16 proportional to the phase difference between the f_(REF) inputsignal 12 and RF CW signal 29. The resultant PE signal is then low passfiltered using low pass filter 18 to yield a slow varying frequencycommand signal 20.

The frequency command signal is input to a controlled oscillator circuit22, typically a voltage controlled oscillator (VCO) or a digitallycontrolled oscillator (DCO). This oscillator generates an RF signal 24,the frequency of which roughly depends linearly on the frequency commandsignal. The oscillator uses a resonator 26 that oscillates in thedesired frequency band. Resonator circuits can be inductor-capacitorbased (LC) or closed loop inverter chains (ring). The output of theoscillator 22 is the phase locked LO signal f_(LO) or f_(RF) which alsoundergoes division by N using divider 28 to generate the feedback signal29 to the phase detector.

A major problem associated with LO generation schemes such as that ofFIG. 1 is their susceptibility to RF signal interference. In particular,the resonator used in the circuit (especially inductor based resonators)often picks-up unwanted RF signals and the resonator frequency can beseverely perturbed. This phenomenon is known as frequency pulling and isdefined as an effect that forces the frequency of an oscillator orresonant frequency to change from a desired value. Causes of the pullinginclude undesired coupling to another frequency source (e.g., RFintermediate or output signals) or the influence of changes in theoscillator load impedance. Typically, the interferer is either themodulated amplified output RF signal, its harmonics in transmitters orthe amplified received signal in receivers. To avoid frequency pulling,a well defined RF transceiver system is built such that the actualresonation frequency of the resonator is neither the output RFfrequency, nor any of its harmonics or sub-harmonics.

In the case of a mobile wireless system, for example, transmitters thatmodulate a non-constant envelope signal require a non-integer ratiobetween the local oscillator frequency and the RF frequency in order toovercome the pulling effect of the power amplifier's output harmonics.Transmission of a wideband signal in high frequency bands such as 5 GHz,however, requires complicated converters that run at very highfrequencies.

A block diagram illustrating an example prior art ½X local oscillatorgeneration scheme is shown in FIG. 2. The example circuit, generallyreferenced 170, comprises a synthesizer at ½ f_(RF), X2 frequencydoubler 176 and polyphase filter 180. In this example LO generationcircuit, the input reference frequency f_(REF) 171 is input tosynthesizer 172 tuned to exactly ½ the RF frequency ½ f_(RF). The outputsignal 174 is then input to a frequency doubler 176 to generate a signalat f_(RF). This signal is then filtered via polyphase filter 180 toyield I and Q (i.e. separated by 90 degrees, also referred to asquadrature) output clock signals f_(LOI) 182 and f_(LOQ) 184,respectively, at f_(RF). The polyphase filter is needed in order togenerate the quadrature output signals. An advantage of this scheme isthe fact that the actual oscillation frequency is not the final outputfrequency but is half. Although the circuit generates f_(RF) signals, amajor disadvantage of using the polyphase filter is that they aretypically large and inaccurate filters causing a potentially large IQmismatch, i.e. LOI and LOQ are not strictly 90 degrees apart. If such asynthesizer solution is inductor based then halving the frequency forcesthe size of the inductors to increase significantly.

A block diagram illustrating an example prior art 2X local oscillatorgeneration scheme is shown in FIG. 3. The well known and widely used LOgeneration scheme (2X scheme), generally referenced 190, comprisessynthesizer 194 and frequency divider 198. A crystal oscillatorgenerated reference signal 192 is input to a synthesizer 194 tunedexactly to twice the RF frequency (2 f_(RF)). The resultant outputsignal 196 is then divided by two using a frequency divider 198 togenerate two signals having a quadrature relationship, i.e. I and Qoutput signals f_(LOI) 200 and f_(LOQ) 202, respectively, at f_(RF).

These signals can be used to modulate or demodulate a signal using amixer pair in a zero IF (ZIF) or a near zero IF (NZIF) scheme. Theadvantages of this scheme is the fact that the actual oscillationfrequency is not the final output frequency but its double and that itis relatively easy to generate a clean quadrature pair f_(LOI) andf_(LOQ) using a frequency divider 198.

Two major disadvantages of this scheme, however, are (1) the fact thatthe second harmonic of the amplified RF signal at 2 f_(RF) can pull theoscillator away, since there could be a small offset between these twofrequencies due to data modulation and (2) that the oscillator must bedesigned to twice the frequency (generally design at high frequenciestends to be more difficult). The first disadvantage can manifest itselfin second harmonic leakage from the system output coupling back into theheart of the resonator or the first harmonic coupling back into thesynthesizer supply circuitry and generating the second harmonic using anon-linear effect and creating frequency pulling. Another manifestationof this disadvantage can be in the receiver where a high gain version ofthe input signal at f_(RF), when compressing a certain stage of thereception chain can create a second harmonic, which will also pull theoscillator (i.e. injection pulling or, worse, injection locking).Injection locking occurs when the oscillations of a first systeminfluences a second system to the extent where the second system nolonger oscillates at its own natural frequency but rather at thefrequency of the first system. In the case of injection pulling, thesecond system can still oscillate at its own natural frequency, butcontains energy at the frequency of the first system. For near-zero IFsystems, such injection locking can cause the oscillator to be pulleddown or up to the actual RF frequency thus making the system effectivelya poorly designed zero-IF system.

To avoid these disadvantages, the LO can be generated at a rationalmultiplier of the output RF frequency. A block diagram illustrating anexample prior art local oscillator generation scheme that generates theLO at a rational multiplier ( 4/3 f_(RF) in this example) of the outputRF frequency is shown in FIG. 4. The prior art LO generation circuit,generally referenced 210, generates the LO at a rational multiplier ofthe output RF frequency and uses dividers and mixers to generate theoutput RF frequency. The circuit 210 comprises a synthesizer 214,frequency dividers 216, 220, multipliers 222, 224 and band pass filters(BPF) 226, 228.

The scheme of FIG. 4 is typically known as an offset-LO generator. Acrystal oscillator output reference signal 212 is input to a synthesizer(PLL) tuned to exactly 4/3 f_(RF). Its output signal is divided by twousing frequency divider 216 to yield a signal at ⅔ f_(RF) 218. Thissignal is divided by two again using frequency divider 220 to yield aquadrature signal pair 221, 223 at ⅓ f_(RF). Signals 221, 223 are mixedwith signal 218 separately via analog mixers 222, 224, respectively. Dueto the multiplicative nature of the mixer it generates a product atf_(RF) (its inputs having frequencies of ⅓ f_(RF) and ⅔ f_(RF)) whilesignals 221, 223 also have a 90 degree phase difference at f_(RF) andthus constitute a quadrature pair. Since the mixer is not ideal,however, undesired frequency products at n/3 f_(RF) (where n is aninteger, n≠3) will also be present at the output of the mixers. Bandpass filters 226, 228 attenuate these unwanted products yielding thefinal LO_(I) (f_(LOI)) 230, LO_(Q) (f_(LOQ)) 233 signals, respectively.

An advantage of the offset LO scheme 210 is that it is able to generatean LO signal at f_(RF), while the resonator oscillates at a rationalmultiple of f_(RF) rather than an integer multiple. Hence, no harmonicsof the output frequency can interfere with the proper operation of theoscillator. While this circuit generally avoids the frequency pullingphenomena described supra, it has a significant disadvantage in theunwanted products (i.e. spurs) generated by the mixers. These productslikely cause spectral emission mask (SEM) violations in the transmitterand can downconvert unwanted jammers or blockers in the receiver. Hence,the spur attenuation or filtering requirement for BPFs 226 and 228 isusually very significant.

It is thus desirable to have a local oscillator generation mechanismthat overcomes the disadvantage of the prior art techniques. The localoscillator generation mechanism should preferably be implementable as anall digital circuit and oscillate at a rational RF frequency multiplier(n/m f_(RF)) so as to avoid frequency pulling while reducing oralleviating the need for a stringent BPF. Further, the local oscillatorgeneration mechanism should enable wideband modulation, such as forpolar modulation, requiring a relatively simple, all digitalimplementation.

SUMMARY OF THE INVENTION

The present invention is a novel and useful apparatus for and method oflocal oscillator (LO) generation with non-integer multiplication ratiobetween the local oscillator and RF frequencies. The LO generationschemes presented herein are operative to generate I and Q square wavesat a designated frequency while avoiding the well known issue ofharmonic pulling.

The novel LO synthesis schemes described herein are suitable for use inany application requiring the generation of a local oscillator signalhaving a non-integer multiplication ratio between the local oscillatorsignal and the output RF frequencies. An example application is providedof a single chip radio, e.g., Bluetooth, GSM, etc., that integrates theRF circuitry with the digital base band (DBB) circuitry on the same dieor on close proximity thereto such that frequency pulling wouldotherwise occur if not for the use of the present invention.

In a first LO generation scheme, the basic PLL structure runs at 4/3 thedesired frequency f_(RF). This frequency is divided by two to obtainin-phase and quadrature square waves at ⅔ f_(RF). The in-phase signal isdivided by two again to obtain in-phase and quadrature square waves at ⅓f_(RF). The signals are then logically combined (i.e. combined usingdigital logic) using XOR operations to obtain I and Q branch signalscontaining spectral spurs. Since the spurs are located in non-disturbingbands, they can be filtered out.

One of the major advantages of this first scheme is that although a“mixing” occurs at a rate of ¼ f_(LO), side-bands at a relative distanceof ¼ f_(LO) are avoided. This is achieved without the need for imagerejection mixing, thus avoiding another well known problem of timing andamplitude mismatches. Further, most of the operations in the LOgeneration scheme are implemented digitally utilizing an ADPLL andfollowed by two divide by two operations and a digital mixer usinglogical gates.

In a second LO generation scheme, the use of analog mixers of the priorart is avoided and replaced with an XOR gate configured to generate thecorrect average frequency. The edges are dynamically adjusted by ±T/12or zero based on the state of the controlled oscillator down-dividedclock.

In a third LO generation scheme, the signal is input to a synthesizertimes to a rational multiplier of the RF frequency f_(RF). The signal isthen divided to generate a plurality of phases of the divided signal. Aplurality of combination signals are generated which are then multipliedby a set of weights and summed to cancel out some undersired products.The result is filtered to generate the LO output signal.

In a fourth LO generation scheme, the signal is input to a synthesizertimes to a rational multiplier of the RF frequency L/N f_(RF). The clocksignal is then divided by a factor Q to form 2Q phases of the clock at afrequency of L(N*Q) f_(RF). Each phase then undergoes division by L. Thephase signals are input to a pulse generator which outputs a pluralityof pulses. The pulses are input to a selector which selects which signalto output at any point in time. By controlling the selector, the outputclock is generated as a TDM based signal. Any spurs are removed by anoptional filter.

In a fifth LO generation scheme, the input baseband signal isinterpolated and upconverted in the digital domain to an IF. The LOoperates at a frequency which is a n/m division of the target RFfrequency f_(RF). The IF frequency is configured to ½ of the LOfrequency. The upconverted IF signal is then converted to the analogdomain via digital power amplifiers followed by voltage combiners. Theoutput of the combiners is band pass filtered to extract the desiredreplica.

Advantages of the LO generation schemes of the present invention include(1) ensuring that no frequency pulling effects occur since the LOfrequency is equal to a non-integer multiple of the RF output frequency;(2) the schemes presented herein are applicable to numerous standardssuch as PFDM, etc.; and (3) the schemes allow for simpler implementationof a DRP based radio at high frequency bands.

Note that some aspects of the invention described herein may beconstructed as software objects that are executed in embedded devices asfirmware, software objects that are executed as part of a softwareapplication on either an embedded or non-embedded computer system suchas a digital signal processor (DSP), microcomputer, minicomputer,microprocessor, etc. running a real-time operating system such as WinCE,Symbian, OSE, Embedded LINUX, etc. or non-real time operating systemsuch as Windows, UNIX, LINUX, etc., or as soft core realized HDLcircuits embodied in an Application. Specific Integrated Circuit (ASIC)or Field Programmable Gate Array (FPGA), or as functionally equivalentdiscrete hardware components. There is thus provided in accordance withthe invention, an apparatus for generating a local oscillator signalhaving an output frequency, comprising an oscillator circuit operativeto generate a first signal, the first signal having a frequencysubstantially equal to a rational multiplier L/N of the outputfrequency, a frequency divide by Q coupled to receive the first signaland operative to generate 2Q second signal phases at a frequencysubstantially equal to a rational multiplier L/(N*Q) of the outputfrequency, a pulse generator operative to generate a plurality of pulsesignals from the 2Q second signal phases, a frequency divider by Lcoupled to receive the 2Q second signal phases and operative to generatea plurality of third signals, a selector operative to select, using timedivision multiplexing, one of the plurality of pulse signals as anoutput signal in accordance with a select control signal, the outputsignal having a frequency substantially equal to the output frequencyand control means for generating the select control signal as a functionof the plurality of third signals and the output signal.

There is also provided in accordance with the invention, a method ofgenerating a local oscillator signal having an output frequency, themethod comprising the steps of generating a first signal at a firstfrequency, the first signal having a frequency substantially equal to arational multiplier L/N of the output frequency, dividing the firstsignal by Q to generate 2Q second signal phases at a frequencysubstantially equal to a rational multiplier L/(N*Q) of the outputfrequency, generating a plurality of pulse signals from the 2Q secondsignal phases, dividing each of the 2Q second signal phases by L togenerate a plurality of third signals and selecting, using time divisionmultiplexing, one of the plurality of pulse signals as an output signalhaving a frequency substantially equal to the output frequency, whereinthe selection determined as a function of the plurality of third signalsand the output signal.

There is further provided in accordance with the invention, an apparatusfor generating a local oscillator signal having an output frequency,comprising an oscillator circuit operative to generate a first signal,the first signal having a frequency substantially equal to a rationalmultiplier L/N of the output frequency, a frequency divider by Q coupledto receive the first signal and operative to generate 2Q second signalphases at a frequency substantially equal to a rational multiplierL/(N*Q) of the output frequency, a multiplexer coupled to receive the 2Qsecond signal phases and operative to output one of the 2Q second signalphases as an output signal in accordance with a select control input anda modulo-2Q counter operative to generate an output coupled to theselect control input, wherein the output of the counter causes themultiplexer to sequentially cycle through the 2Q second signal phasessuch that the output signal substantially resembles a desired outputclock signal.

There is also provided in accordance with the invention, an apparatusfor generating a local oscillator signal having an output frequency,comprising an oscillator circuit operative to generate a quadratureclock of four substantially equally spaced phases, the quadrature clockhaving a frequency substantially equal to a rational multiplier ¾ of theoutput frequency, a multiplexer coupled to receive the quadrature clockand operative to output one of the four phases as an output signal inaccordance with a select control input and a modulo-4 counter operativeto generate an output coupled to the select control input, wherein theoutput of the counter causes the multiplexer to sequentially cyclethrough the four phases of the quadrature clock.

There is further provided in accordance with the invention, a radiocomprising a transmitter coupled to an antenna, the transmittercomprising a local oscillator having an output frequency, the localoscillator comprising an oscillator circuit operative to generate afirst signal, the first signal having a frequency substantially equal toa rational multiplier L/N of the output frequency, a frequency dividerby Q coupled to receive the first signal and operative to generate 2Qsecond signal phases at a frequency substantially equal to a rationalmultiplier L/(N*Q) of the output frequency, a pulse generator operativeto generate a plurality of pulse signals from the 2Q second signalphases, a frequency divide by L coupled to receive the 2Q second signalphases and operative to generate a plurality of third signals, aselector operative to select, using time division multiplexing, one ofthe plurality of pulse signals as an output signal in accordance with aselect control signal, the output signal having a frequencysubstantially equal to the output frequency, control means forgenerating the select control signal as a function of the plurality ofthird signals and the output signal, a receiver coupled to the antennaand a baseband processor coupled to the transmitter and the receiver.

There is also provided in accordance with the invention, a radiocomprising a transmitter coupled to an antenna, the transmittercomprising a local oscillator having an output frequency, the localoscillator comprising an oscillator circuit operative to generate afirst signal, the first signal having a frequency substantially equal toa rational multiplier L/N of the output frequency, a frequency divide byQ coupled to receive the first signal and operative to generate 2Qsecond signal phases at a frequency substantially equal to a rationalmultiplier L/(N*Q) of the output frequency, a multiplexer coupled toreceive the 2Q second signal phases and operative to output one of the2Q second signal phases as an output signal in accordance with a selectcontrol input, a modulo-2Q counter operative to generate an outputcoupled to the select control input, wherein the output of the countercauses the multiplexer to sequentially cycle through the 2Q secondsignal phases such that the output signal substantially resembles adesired output clock signal, a receiver coupled to the antenna and abaseband processor coupled to the transmitter and the receiver.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is herein described, by way of example only, withreference to the accompanying drawings, wherein:

FIG. 1 is a block diagram illustrating an example prior art phase lockedlook (PLL) local oscillator (LO) generator circuit;

FIG. 2 is a block diagram illustrating an example prior art ½X localoscillator generation scheme;

FIG. 3 is a block diagram illustrating an example prior art 2X localoscillator generation scheme;

FIG. 4 is a block diagram illustrating an example prior art localoscillator generation scheme that generates the LO at a rationalmultiplier of the output RF frequency;

FIG. 5 is a block diagram illustrating a single chip polar transceiverradio incorporating an all-digital local oscillator based transmitterand receiver and local oscillator (LO) generation mechanism of thepresent invention;

FIG. 6 is a simplified block diagram illustrating an example mobilecommunication device incorporating the local oscillator generationmechanism of the present invention;

FIG. 7 is a block diagram illustrating an example all digital phaselocked loop (ADPLL) incorporating the local oscillator generationmechanism of the present invention;

FIG. 8 is a block diagram illustrating a first embodiment of the localoscillator generation mechanism of the present invention employing anoffset LO generator;

FIG. 9 is a timing diagram illustrating the various digital traces forthe first embodiment local oscillator generation mechanism of thepresent invention shown in FIG. 8;

FIG. 10 is a graph illustrating the spectrum magnitude plot of theoutput of the circuit of FIG. 8;

FIG. 11 is a block diagram illustrating a second embodiment of the localoscillator generation mechanism of the present invention;

FIG. 12 is a timing diagram illustrating the various time domain tracesfor the second embodiment local oscillator generation mechanism of thepresent invention shown in FIG. 11;

FIG. 13 is a block diagram illustrating a third embodiment of the localoscillator generation mechanism of the present invention;

FIG. 14 is a block diagram illustrating a fourth embodiment of the localoscillator generation mechanism of the present invention;

FIG. 15 is a block diagram illustrating a fifth embodiment of the localoscillator generation mechanism of the present invention;

FIG. 16 is a phasor diagram illustrating the relationship between theproducts generated in the LO generation circuit of FIG. 15;

FIG. 17 is a timing diagram illustrating the various time domain tracesfor the fifth embodiment local oscillator generation mechanism of thepresent invention shown in FIG. 15;

FIG. 18 is a graph illustrating the spectrum magnitude plot of theoutput of the circuit of FIG. 15;

FIG. 19 is a block diagram illustrating a sixth embodiment of the localoscillator generation mechanism of the present invention;

FIG. 20 is a block diagram illustrating a seventh embodiment of thelocal oscillator generation mechanism of the present invention;

FIG. 21 is a timing diagram illustrating the various time domain tracesfor the seventh embodiment local oscillator generation mechanism of thepresent invention shown in FIG. 20;

FIG. 22 is a graph illustrating the spectrum magnitude plot of theoutput of the circuit of FIG. 20;

FIG. 23 is a block diagram illustrating an eighth embodiment of thelocal oscillator generation mechanism of the present invention;

FIG. 24 is a timing diagram illustrating the various time domain tracesfor the eighth embodiment local oscillator generation mechanism of thepresent invention shown in FIG. 23;

FIG. 25 is a graph illustrating the spectrum magnitude plot of theoutput of the circuit of FIG. 23;

FIG. 26 is a block diagram illustrating a ninth embodiment of the localoscillator generation mechanism of the present invention incorporatingthe Cartesian based non-integer local oscillator;

FIG. 27 is a simplified block diagram illustrating the DPA of the localoscillator generation circuit of FIG. 26 in more detail; and

FIG. 28 is a graph illustrating simulation results of the spectrum atthe output of the transmitter employing the Cartesian based non-integerlocal oscillator of FIG. 26.

DETAILED DESCRIPTION OF THE INVENTION Notation Used Throughout Thefollowing notation is used throughout this document.

Term Definition AC Alternating Current ACL Asynchronous ConnectionlessLink ACW Amplitude Control Word ADC Analog to Digital Converter ADPLLAll Digital Phase Locked Loop AM Amplitude Modulation ASIC ApplicationSpecific Integrated Circuit AVI Audio Video Interface AWS AdvancedWireless Services BIST Built-In Self Test BMP Windows Bitmap BPF BandPass Filter CMOS Complementary Metal Oxide Semiconductor CPU CentralProcessing Unit CU Control Unit CW Continuous Wave DAC Digital to AnalogConverter dB Decibel DBB Digital Baseband DC Direct Current DCODigitally Controlled Oscillator DCXO Digitally Controlled CrystalOscillator DPA Digitally Controlled Power Amplifier DRAC Digital to RFAmplitude Conversion DRP Digital RF Processor or Digital Radio ProcessorDSL Digital Subscriber Line DSP Digital Signal Processor EDGE EnhancedData Rates for GSM Evolution EDR Enhanced Data Rate EEPROM ElectricallyErasable Programmable Read Only Memory EPROM Erasable Programmable ReadOnly Memory eSCO Extended Synchronous Connection-Oriented FCC FederalCommunications Commission FCW Frequency Command Word FIB Focused IonBeam FM Frequency Modulation FPGA Field Programmable Gate Array GMSKGaussian Minimum Shift Keying GPS Global Positioning System GSM GlobalSystem for Mobile communications HB High Band HDL Hardware DescriptionLanguage HFP Hands Free Protocol I/F Interface IC Integrated CircuitIEEE Institute of Electrical and Electronics Engineers IIR InfiniteImpulse Response JPG Joint Photographic Experts Group LAN Local AreaNetwork LB Low Band LDO Low Drop Out LO Local Oscillator LPF Low PassFilter MAC Media Access Control MAP Media Access Protocol MBOA MultibandOFDM Alliance MIM Metal Insulator Metal Mod Modulo MOS Metal OxideSemiconductor MP3 MPEG-1 Audio Layer 3 MPG Moving Picture Experts GroupMUX Multiplexer NZIF Near Zero IF OFDM Orthogonal Frequency DivisionMultiplexing PA Power Amplifier PAN Personal Area Network PC PersonalComputer PCI Personal Computer Interconnect PD Phase Detector PDAPersonal Digital Assistant PE Phase Error PHE Phase Error PLL PhaseLocked Loop PM Phase Modulation PPA Pre-Power Amplifier QoS Quality ofService RAM Random Access Memory RF Radio Frequency RFBIST RF Built-InSelf Test RMS Root Mean Squared ROM Read Only Memory SAM Sigma-DeltaAmplitude Modulation SAW Surface Acoustic Wave SCO SynchronousConnection-Oriented SEM Spectral Emission Mask SIM Subscriber IdentityModule SoC System on Chip SRAM Static Read Only Memory SYNTH SynthesizerTDC Time to Digital Converter TDD Time Division Duplex TV Television UGSUnsolicited Grant Services USB Universal Serial Bus UWB Ultra WidebandVCO Voltage Controlled Oscillator WCDMA Wideband Code Division MultipleAccess WiFi Wireless Fidelity WiMAX Worldwide Interoperability forMicrowave Access WiMedia Radio platform for UWB WLAN Wireless Local AreaNetwork WMA Windows Media Audio WMAN Wireless Metropolitan Area NetworkWMV Windows Media Video WPAN Wireless Personal Area Network XORExclusive Or ZIF Zero IF

Detailed Description of the Invention

The present invention is a novel and useful apparatus for and method oflocal oscillator (LO) generation with non-integer multiplication ratiobetween the local oscillator and RF output frequencies. The invention issuitable for use in any application requiring the generation of a localoscillator signal having a non-integer multiplication ratio between thelocal oscillator signal and the output RF frequencies. An exampleapplication is provided of a single chip radio that integrates the RFcircuitry with the digital base band (DBB) circuitry on the same die oron close proximity thereto such that frequency pulling would otherwiseoccur if not for the use of the present invention.

Although the LO generation mechanism is applicable to numerous wirelesscommunication standards and can be incorporated in numerous types ofwireless or wired communication devices such a multimedia player, mobilestation, cellular phone, PDA, DSL modem, WPAN device, etc., it isdescribed in the context of a digital RF processor (DRP) basedtransmitter that may be adapted to comply with a particular wirelesscommunications standard such as GSM, Bluetooth, EDGE, WCDMA, WLAN,WiMax, etc. It is appreciated, however, used in optical, wired andwireless applications. Further, the invention is not limited to use witha specific modulation scheme but is applicable to any modulation schemeincluding both digital and analog modulations where there is a need tomitigate the frequency pulling effect of the RF output frequency on thereference frequency clock generation.

Note that throughout this document, the term communications device isdefined as any apparatus or mechanism adapted to transmit, receive ortransmit and receive data through a medium. The term communicationstransceiver or communications device is defined as any apparatus ormechanism adapted to transmit and receive data through a medium. Thecommunications device or communications transceiver may be adapted tocommunicate over any suitable medium, including wireless or wired media.Examples of wireless media include RF, infrared, optical, microwave,UWB, Bluetooth, WiMAX, WiMedia, WiFi, or any other broadband medium,etc. Examples of wired media include twisted pair, coaxial, opticalfiber, any wired interface (e.g., USB, Firewire, Ethernet, etc.). Theterm Ethernet network is defined as a network compatible with any of theIEEE 802.3 Ethernet standards, including but not limited to 10Base-T,100Base-T or 1000Base-T over shielded or unshielded twisted pair wiring.The terms communications channel, link and cable are usedinterchangeably. The notation DRP is intended to denote either a DigitalRF Processor or Digital Radio Processor. References to a Digital RFProcessor infer a reference to a Digital Radio Processor and vice versa.

The term multimedia player or device is defined as any apparatus havinga display screen and user input means that is capable of playing audio(e.g., MP3, WMA, etc.), video (AVI, MPG, WMV, etc.) and/or pictures(JPG, BMP, etc.). The user input means is typically formed of one ormore manually operated switches, buttons, wheels or other user inputmeans. Examples of multimedia devices include pocket sized personaldigital assistants (PDAs), personal media player/recorders, cellulartelephones, handheld devices, and the like.

Some portions of the detailed descriptions which follow are presented interms of procedures, logic blocks, processing, steps, and other symbolicrepresentations of operations on data bits within a computer memory.These descriptions and representations are the means used by thoseskilled in the data processing arts to most effectively convey thesubstance of their work to others skilled in the art. A procedure, logicblock, process, etc., is generally conceived to be a self-consistentsequence of steps or instructions leading to a desired result. The stepsrequire physical manipulations of physical quantities. Usually, thoughnot necessarily, these quantities take the form of electrical ormagnetic signals capable of being stored, transferred, combined,compared and otherwise manipulated in a computer system. It has provenconvenient at times, principally for reasons of common usage, to referto these signals as bits, bytes, words, values, elements, symbols,characters, terms, numbers, or the like.

It should be born in mind that all of the above and similar terms are tobe associated with the appropriate physical quantities they representand are merely convenient labels applied to these quantities. Unlessspecifically stated otherwise as apparent from the followingdiscussions, it is appreciated that throughout the present invention,discussions utilizing terms such as ‘processing,’ ‘computing,’‘calculating,’ ‘determining,’ ‘displaying’ or the like, refer to theaction and processes of a computer system, or similar electroniccomputing device, that manipulates and transforms data represented asphysical (electronic) quantities within the computer system's registersand memories into other data similarly represented as physicalquantities within the computer system memories or registers or othersuch information storage, transmission or display devices.

The invention can take the form of an entirely hardware embodiment, anentirely software embodiment or an embodiment containing a combinationof hardware and software elements. In one embodiment, a portion of themechanism of the invention is implemented in software, which includesbut is not limited to firmware, resident software, object code, assemblycode, microcode, etc.

Furthermore, the invention can take the form of a computer programproduct accessible from a computer-usable or computer-readable mediumproviding program code for use by or in connection with a computer orany instruction execution system. For the purposes of this description,a computer-usable or computer readable medium is any apparatus that cancontain, store, communicate, propagate, or transport the program for useby or in connection with the instruction execution system, apparatus, ordevice, e.g., floppy disks, removable hard drives, computer filescomprising source code or object code, flash semiconductor memory (USBflash drives, etc.), ROM, EPROM, or other semiconductor memory devices.

Single Chip Radio

A block diagram illustrating a single chip polar transceiver radioincorporating an all-digital local oscillator based transmitter andreceiver and local oscillator (LO) generation mechanism of the presentinvention is shown in FIG. 5. For illustration purposes only, thetransmitter, as shown, is adapted for the GSM/EDGE/WCDMA cellularstandards. It is appreciated, however, that one skilled in thecommunication arts can adapt the transmitter illustrated herein to othermodulations and communication standards as well without departing fromthe spirit and scope of the present invention.

The radio, generally referenced 30, comprises a radio integrated circuit31 coupled to a crystal 38, front end module 46 coupled to an antenna44, and battery management circuit 32 coupled to battery 68. The radiochip 31 comprises a script processor 60, digital baseband (DBB)processor 61, memory 62 (e.g., static RAM), TX block 42, RX block 58,digitally controlled crystal oscillator (DCXO) 50, slicer 51, powermanagement unit 34 and RF built-in self test (BIST) 36. The TX blockcomprises high speed and low speed digital logic block 40 including ΣΔmodulators 52, 54, digitally controlled oscillator (DCO) 56, non-integerdivider block 59 and digitally controlled power amplifier (DPA) 48. TheRX block comprises a low noise transconductance amplifier 63, currentsampler 64, discrete time processing block 65, analog to digitalconverter (ADC) 66 and digital logic block 67.

The principles presented herein have been used to develop threegenerations of a Digital RF Processor (DRP): single-chip Bluetooth, GSMand GSM/EDGE radios realized in 130 nm, 90 nm and 65 nm digital CMOSprocess technologies, respectively. This architecture is also used asthe foundation for a UMTS single-chip radio manufactured using a 45 nmCMOS process. The common architecture is highlighted in FIG. 5 withfeatures added specific to the cellular radio. The all digital phaselocked loop (ADPLL) based transmitter employs a polar architecture withall digital phase/frequency and amplitude modulation paths. The receiveremploys a discrete-time architecture in which the RF signal is directlysampled and processed using analog and digital signal processingtechniques.

A key component is the digitally controlled oscillator (DCO) 56, whichavoids any analog tuning controls. A digitally-controlled crystaloscillator (DCXO) generates a high-quality base station-synchronizedfrequency reference such that the transmitted carrier frequencies andthe received symbol rates are accurate to within 0.1 ppm. Fine frequencyresolution is achieved through high-speed ΣΔ dithering of its varactors.Digital logic built around the DCO realizes an all-digital PLL (ADPLL)that is used as a local oscillator for both the transmitter andreceiver. In accordance with the invention, the output of the DCOundergoes non-integer open-loop division using non-integer divider block59. The polar transmitter architecture utilizes the wideband directfrequency modulation capability of the ADPLL and a digitally controlledpower amplifier (DPA) 48 for the amplitude modulation. The DPA operatesin near-class-E mode and uses an array of nMOS transistor switches toregulate the RF amplitude. It is followed by a matching network and anexternal front-end module 46, which comprises a power amplifier (PA), atransmit/receive switch for the common antenna 44 and RX surfaceacoustic wave (SAW) filters. Fine amplitude resolution is achievedthrough high-speed ΣΔ dithering of the DPA nMOS transistors.

The receiver 58 employs a discrete-time architecture in which the RFsignal is directly sampled at the Nyquist rate of the RF carrier andprocessed using analog and digital signal processing techniques. Thetransceiver is integrated with a script processor 60, dedicated digitalbase band processor 61 (i.e. ARM family processor and/or DSP) and SRAMmemory 62. The script processor handles various TX and RX calibration,compensation, sequencing and lower-rate data path tasks and encapsulatesthe transceiver complexity in order to present a much simpler softwareprogramming model.

The frequency reference (FREF) is generated on-chip by a 26 MHz (or anyother desired frequency, such as 13 or 38.4 MHz) digitally controlledcrystal oscillator (DCXO) 50 coupled to slicer 51. The output of theslicer is input to the TDC circuit 69.

An integrated power management (PM) system 34 is connected to anexternal battery management circuit 32 that conditions and stabilizesthe supply voltage. The PM comprises multiple low drop out (LDO)regulators that provide internal supply voltages and also isolate supplynoise between circuits, especially protecting the DCO. The RF built-inself-test (RFBIST) 36 performs autonomous phase noise and modulationdistortion testing, various loopback configurations for bit-error ratemeasurements and implements the DPA calibration and BIST mechanism. Thetransceiver is integrated with the digital baseband, SRAM memory in acomplete system-on-chip (SoC) solution. Almost all the clocks on thisSoC are derived from and are synchronous to the RF oscillator clock.This helps to reduce susceptibility to the noise generated throughclocking of the massive digital logic.

The transmitter comprises a polar architecture in which the amplitudeand phase/frequency modulations are implemented in separate paths.Transmitted symbols generated in the digital baseband (DBB) processorare first pulse-shape filtered in the Cartesian coordinate system. Thefiltered in-phase (I) and quadrature (Q) samples are then convertedthrough a CORDIC algorithm into amplitude and phase samples of the polarcoordinate system. The phase is then differentiated to obtain frequencydeviation. The polar signals are subsequently conditioned through signalprocessing to sufficiently increase the sampling rate in order to reducethe quantization noise density and lessen the effects of the modulatingspectrum replicas.

A more detailed description of the operation of the ADPLL can be foundin U.S. Patent Publication No. 2006/0033582A1, published Feb. 16, 2006,to Staszewski et al., entitled “Gain Calibration of a Digital ControlledOscillator,” U.S. Patent Publication No. 2006/0038710A1, published Feb.23, 2006, Staszewski et al., entitled “Hybrid Polar/Cartesian DigitalModulator” and U.S. Pat. No. 6,809,598, to Staszewski et al., entitled“Hybrid Of Predictive And Closed-Loop Phase-Domain Digital PLLArchitecture,” all of which are incorporated herein by reference intheir entirety.

Mobile Device/Cellular Phone/PDA System

A simplified block diagram illustrating an example mobile communicationdevice incorporating the local oscillator generation mechanism of thepresent invention is shown in FIG. 6. The communication device maycomprise any suitable wired or wireless device such as a multimediaplayer, mobile station, mobile device, cellular phone, PDA, wirelesspersonal area network (WPAN) device, Bluetooth EDR device, etc. Forillustration purposes only, the communication device is shown as acellular phone or smart phone. Note that this example is not intended tolimit the scope of the invention as the LO generation mechanism of thepresent invention can be implemented in a wide variety of wireless andwired communication devices.

The cellular phone, generally referenced 70, comprises a basebandprocessor or CPU 71 having analog and digital portions. The basiccellular link is provided by the RF transceiver 94 and related one ormore antennas 96, 98. A plurality of antennas is used to provide antennadiversity which yields improved radio performance. The cell phone alsocomprises internal RAM and ROM memory 110, Flash memory 112 and externalmemory 114.

In accordance with the invention, the RF transceiver comprises anon-integer LO divider block 97 that generates an RF frequency f_(RF)where the RF output frequency is a non-integer multiple of the LOcircuit frequency, as described in more detail infra. In operation, theLO generation mechanism may be implemented as hardware, as softwareexecuted as a task on the baseband processor 71 or a combination ofhardware and software. Implemented as a software task, the program codeoperative to implement the frequency generation mechanism of the presentinvention is stored in one or more memories 110, 112 or 114.

Several user interface devices include microphone 84, speaker 82 andassociated audio codec 80, a keypad for entering dialing digits 86,vibrator 88 for alerting a user, camera and related circuitry 100, a TVtuner 102 and associated antenna 104, display 106 and associated displaycontroller 108 and GPS receiver 90 and associated antenna 92.

A USB interface connection 78 provides a serial link to a user's PC orother device. An FM receiver 72 and antenna 74 provide the user theability to listen to FM broadcasts. WLAN radio and interface 76 andantenna 77 provide wireless connectivity when in a hot spot or withinthe range of an ad hoc, infrastructure or mesh based wireless LANnetwork. A Bluetooth EDR radio and interface 73 and antenna 75 provideBluetooth wireless connectivity when within the range of a Bluetoothwireless network. Further, the communication device 70 may also comprisea WiMAX radio and interface 123 and antenna 125. SIM card 116 providesthe interface to a user's SIM card for storing user data such as addressbook entries, etc. The communication device 70 also comprises an UltraWideband (UWB) radio and interface 83 and antenna 81. The UWB radiotypically comprises an MBOA-UWB based radio.

Portable power is provided by the battery 124 coupled to batterymanagement circuitry 122. External power is provided via USB power 118or an AC/DC adapter 120 connected to the battery management circuitrywhich is operative to manage the charging and discharging of the battery124.

ADPLL Polar Transmitter Incorporating LO Generation Mechanism

A block diagram illustrating an ADPLL-based polar transmitter forwireless applications incorporating the LO generation mechanism of thepresent invention is shown in FIG. 7. A more detailed description of theoperation of the ADPLL can be found in U.S. Patent Publication No.2006/0033582A1, published Feb. 16, 2006, to Staszewski et al., entitled“Gain Calibration of a Digital Controlled Oscillator,” U.S. PatentPublication No. 2006/0038710A1, published Feb. 23, 2006, Staszewski etal., entitled “Hybrid Polar/Cartesian Digital Modulator” and U.S. Pat.No. 6,809,598, to Staszewski et al., entitled “Hybrid Of Predictive AndClosed-Loop Phase-Domain Digital PLL Architecture,” all of which areincorporated herein by reference in their entirety.

For illustration purposes only, the transmitter, as shown, is adaptedfor the GSM/EDGE/WCDMA cellular standards. It is appreciated, however,that one skilled in the communication arts can adapt the transmitterillustrated herein to other modulations and communication standards aswell without departing from the spirit and scope of the presentinvention.

The transmitter, generally referenced 130, is well-suited for adeep-submicron CMOS implementation. The transmitter comprises a complexpulse shaping filter 168, amplitude modulation (AM) block 169 and ADPLL132. The circuit 130 is operative to perform complex modulation in thepolar domain in addition to the generation of the local oscillator (LO)signal for the receiver. All clocks in the system are derived directlyfrom this source. Note that the transmitter is constructed using digitaltechniques that exploit the high speed and high density of the advancedCMOS, while avoiding problems related to voltage headroom. The ADPLLcircuit replaces a conventional RF synthesizer architecture (based on avoltage-controlled oscillator (VCO) and a phase/frequency detector andcharge-pump combination), with a digitally controlled oscillator (DCO)148, a time-to-digital converter (TDC) 162 and a non-integer LO divider134. All inputs and outputs are digital and some even at multi-GHzfrequency.

The core of the ADPLL is a digitally controlled oscillator (DCO) 148adapted to generate the RF oscillator clock CKV. The oscillator core(not shown) operates at a rational multiplier of the 1.6-2.0 GHz (e.g.,4/3) high band frequency or at a rational multiplier of the 0.8-1.0 GHzlow band frequency (e.g., 4/3). The output of the DCO is then dividedusing a non-integer LO divider 134 in accordance with the presentinvention for precise generation of RX quadrature signals, and for useas the transmitter's carrier frequency. The single DCO is shared betweentransmitter and receiver and is used for both the high frequency bands(HB) and the low frequency bands (LB). In addition to the integercontrol of the DCO, at least 3-bits of the minimal varactor size usedare dedicated for ΣΔ dithering in order to improve frequency resolution.The DCO comprises a plurality of varactor banks, which may be realizedas n-poly/n-well inversion type MOS capacitor (MOSCAP) devices or MetalInsulator Metal (MIM) devices that operate in the flat regions of theirC-V curves to assist digital control. The output of the DCO is input tothe non-integer LO divider 134, which generates a modulated digitalsignal at f_(RF). This signal is input to the pre-power amplifier (PPA)152. It is also input to the RF low band pre-power amplifier 154 afterdivide by two via divider 150. Note that alternatively, the loop may beclosed by coupling the signal output of the DCO before the non-integerLO divider to the retimer and TDC circuits.

The expected variable frequency f_(V) is related to the referencefrequency f_(R) by the frequency command word (FCW).

$\begin{matrix}{{{FCW}\lbrack k\rbrack} \equiv \frac{E\left( {f_{V}\lbrack k\rbrack} \right)}{f_{R}}} & (1)\end{matrix}$

The FCW is time variant and is allowed to change with every cycleT_(R)=1/f_(R) of the frequency reference clock. With W_(F)=24 the wordlength of the fractional part of FCW, the ADPLL provides fine frequencycontrol with 1.5 Hz accuracy, according to:

$\begin{matrix}{{\Delta \; f_{res}} = \frac{f_{R}}{2^{W_{F}}}} & (2)\end{matrix}$

The number of integer bits W_(I)=8 has been chosen to fully cover theGSM/EDGE and partial WCDMA band frequency range of f_(V)=1,600-2,000 MHzwith an arbitrary reference frequency f_(R)≧8 MHz.

The ADPLL operates in a digitally-synchronous fixed-point phase domainas follows: The variable phase accumulator 156 determines the variablephase R_(V)[i] by counting the number of rising clock transitions of theDCO oscillator clock CKV as expressed below.

$\begin{matrix}{{R_{V}\lbrack i\rbrack} = {\sum\limits_{l = 0}^{i}1}} & (3)\end{matrix}$

The index i indicates the DCO edge activity. The variable phase R_(V)[i]is sampled via sampler 158 to yield sampled FREF variable phaseR_(V)[k], where k is the index of the FREF edge activity. The sampledFREF variable phase R_(V)[k] is fixed-point concatenated with thenormalized time-to-digital converter (TDC) 162 output ε[k]. The TDCmeasures and quantizes the time differences between the frequencyreference FREF and the DCO clock edges. The sampled differentiated (viablock 160) variable phase is subtracted from the frequency command word(FCW) by the digital frequency detector 138. The frequency errorf_(E)[k] samples

f _(E) [k]=FCW−[(R _(V) [k]−ε[k])−(R _(V) [k−1]−ε[k−1])]  (4)

are accumulated via the frequency error accumulator 140 to create thephase error φ_(E)[k] samples

$\begin{matrix}{{\varphi_{E}\lbrack k\rbrack} = {\sum\limits_{l = 0}^{k}{f_{E}\lbrack k\rbrack}}} & (5)\end{matrix}$

which are then filtered by a fourth order IIR loop filter 142 and scaledby a proportional loop attenuator α. A parallel feed with coefficient ρadds an integrated term to create type-II loop characteristics whichsuppress the DCO flicker noise.

The IIR filter is a cascade of four single stage filters, eachsatisfying the following equation:

y[k]=(1−λ)·y[k−1]+λ·x[k]  (6)

wherein

x[k] is the current input;

y[k] is the current output;

k is the time index;

λ is the configurable coefficient;

The 4-pole IIR loop filter attenuates the reference and TDC quantizationnoise with an 80 dB/dec slope, primarily to meet the GSM/EDGE spectralmask requirements at 400 kHz offset. The filtered and scaled phase errorsamples are then multiplied by the DCO gain K_(DCO) normalization factorf_(R)/{circumflex over (K)}_(DCO) via multiplier 146, where f_(R) is thereference frequency and {circumflex over (K)}_(DCO) is the DCO gainestimate, to make the loop characteristics and modulation independentfrom K_(DCO). The modulating data is injected into two points of theADPLL for direct frequency modulation, via adders 136 and 144. A hitlessgear-shifting mechanism for the dynamic loop bandwidth control serves toreduce the settling time. It changes the loop attenuator α several timesduring the frequency locking while adding the (α₁/α₂−1)φ₁ dc offset tothe phase error, where indices 1 and 2 denote before and after theevent, respectively. Note that φ₁=φ₂, since the phase is to becontinuous.

The frequency reference FREF is input to the retimer 166 and providesthe clock for the TDC 162. The FREF input is resampled by the RFoscillator clock CKV via retimer block 166 which may comprise a flipflop or register clocked by the reference frequency FREF. The resultingretimed clock (CKR) is distributed and used throughout the system. Thisensures that the massive digital logic is clocked after the quietinterval of the phase error detection by the TDC. Note that in theexample embodiment described herein, the ADPLL is a discrete-timesampled system implemented with all digital components connected withall digital signals.

First Embodiment: Non-Harmonic DCO With XOR and BPF (Offset LOGenerator)

In a first LO generation scheme, the basic PLL structure runs at 4/3 thedesired frequency f_(RF). This frequency is divided by two to obtainin-phase and quadrature square waves at ⅔ f_(RF). It is noted that thedivision by two would not be necessary if the quadrature generation ofthe square wave clocks is achieved through some other means. In thiscase, the oscillator could operate at a lower frequency. The in-phasesignal is divided by two again to obtain in-phase and quadrature squarewaves at ⅓ f_(RF). The signals are then logically mixed using XORoperations to obtain I and Q branch signals containing spectral spursevery ((2n+1)/3)f_(RF), where n is an integer. Since the spurs arelocated in non-disturbing bands, they can be filtered out. In adeep-submicron chip, for example, there is a need for a digitalimplementation of the above described LO generation scheme.

A block diagram illustrating a first embodiment of the local oscillatorgeneration mechanism of the present invention employing an offset LOgenerator is shown in FIG. 8. The circuit, generally referenced 240, isa fully digital implementation of an offset LO generator. The circuit240 comprises a synthesizer 244, frequency dividers 246, 252, XOR gates254, 256 and band pass filters 262, 264.

In operation, a reference signal f_(REF) 242 generated by a crystaloscillator is input to a synthesizer 244 tuned to exactly 4/3 f_(RF).The output of the synthesizer is divided by two via divider 246 togenerate a quadrature pair clocks (quadrature 248 and in-phase 250) at ⅔f_(RF). The in-phase signal 250 is further divided via divider 252 intoanother quadrature pair (quadrature 261 and in-phase 263) at ⅓ f_(RF).The quadrature signal 248 is XORed with the quadrature divided signal261 via XOR circuit 254 to generate an in-phase unfiltered LO signal 258having spectral spurs every f_(RF)/2. The in-phase signal 263 is mixedwith the quadrature divided signal 248 via XOR circuit 256 to yield theunfiltered LO quadrature signal 260. Quadrature pair 258, 260 undergoband pass filtering via filters 262, 264 to yield the output localoscillator signals LO_(I) (f_(LOI)) 266, LO_(Q) (f_(LOQ)) 268,respectively.

A timing diagram illustrating the various digital traces for the firstembodiment local oscillator generation mechanism of the presentinvention of FIG. 8 is shown in FIG. 9. Signal I (trace 270) shows thefirst divider 246 in-phase signal 250, while signal Q (trace 272) showsthe first divider 246 quadrature signal 248. These signals have a 90degree phase shift relationship to each other. Signal II (trace 274)shows the in-phase signal 263 output of the second divider 252, whilesignal IQ (trace 276) shows the second divider 252 quadrature output261. Signals I_F_(c) (trace 278) and Q_F_(c) (trace 280) show the timebehavior of the in-phase and quadrature unfiltered LO signals 258 and260, respectively. From the timing diagram, it is evident that thesesignals are not spectrally pure sine waves but have a binary pattern of10110100, sampled at ⅜ T, where T=1/f_(RF).

A graph illustrating the spectrum magnitude plot of the output of thecircuit of FIG. 8 is shown in FIG. 10. In particular, the spectrum showsa power spectrum magnitude plot of signal traces 278 or 280. The plotcomprises the fundamental or desired frequency product at f_(RF) (peak292) as well as undesired products at ((1+2n)/3) f_(RF), where n is aninteger (i.e. peaks 290, 294, 296, 298). The magnitude of the undesiredharmonic 290 at ⅓ f_(RF) is approximately −7 dB, while its counterpartat 5/3 f_(RF) is about −5 dB. The magnitude of the unwanted peaks,creates the need for stringent requirements on BPFs 262, 264.

The basic ADPLL structure (FIG. 7) runs at approximately 3.2 GHz ( 4/3times the desired frequency f_(LO)). As described supra, the LOfrequency is divided by two to obtain in phase and quadrature squarewaves at ⅔ f_(LO) and subsequently divided down again to obtain in-phaseand quadrature square waves at ⅓ f_(LO). A logical type “mixing”operation is then applied using the following equations:

I=NXOR(Q, IQ)

Q=NXOR(II, Q)   (7)

where

nxor(A, B)=AB or AB;

Ā being the logical NOT of A;

Note that the logical combining operation may comprise either NXOR orXOR yielding either the signal or its inverse polarity (i.e. 180 degree)signal. In electrical terms, this means that all the operations from theADPLL up to the band pass filters are carried out by high speed analogcircuits, while the band pass filters are analog in nature followed by aslicer (inverting or non-inverting).

A mathematical derivation for the first embodiment will now bepresented. In the case of no mismatch, writing the Fourier series forthe I signal, we obtain:

$\begin{matrix}{I_{1} = {\frac{2j}{\pi}{\sum\limits_{\underset{n\mspace{14mu} {odd}}{n = {- \infty}}}^{\infty}{\frac{1}{n}^{{j2\pi}\; n\; {ft}}}}}} & (8)\end{matrix}$

where

f denotes the square wave frequency after the first divider;

t denotes time;

j denotes √{square root over (−1)};

Similar results can be obtained for Q, II and IQ.

$\begin{matrix}{Q = {\frac{2j}{\pi}{\sum\limits_{\underset{n\mspace{14mu} {odd}}{n = {- \infty}}}^{\infty}{\frac{1}{n}^{{j2\pi}\; {n{({{ft} - \frac{1}{4}})}}}}}}} & (9) \\{{II} = {\frac{2j}{\pi}{\sum\limits_{\underset{n\mspace{14mu} {odd}}{n = {- \infty}}}^{\infty}{\frac{1}{n}^{{j2\pi}\; n\frac{f}{2}t}}}}} & (10) \\{{IQ} = {\frac{2j}{\pi}{\sum\limits_{\underset{n\mspace{14mu} {odd}}{n = {- \infty}}}^{\infty}{\frac{1}{n}^{{j2\pi}\; {n{({{\frac{f}{2}t} - \frac{1}{4}})}}}}}}} & (11)\end{matrix}$

The NXOR operation is equivalent to time domain multiplication andtherefore the LO_(I) and LO_(Q) signals can be expressed as:

$\begin{matrix}{{LO}_{I} = {{Q \cdot {IQ}} = {\frac{- 4}{\pi^{2}}{\sum\limits_{\underset{n,{m\mspace{14mu} {odd}}}{n,{m = {- \infty}}}}^{\infty}{\frac{1}{nm}^{{j2\pi}{({{{({n + \frac{m}{2}})}{ft}} - {\frac{1}{4}{({n + m})}}})}}}}}}} & (12) \\{{LO}_{Q} = {{{II} \cdot Q} = {\frac{- 4}{\pi^{2}}{\sum\limits_{\underset{n,{m\mspace{14mu} {odd}}}{n,{m = {- \infty}}}}^{\infty}{\frac{1}{nm}^{{j2\pi}{({{{({\frac{n}{2} + m})}{ft}} - {\frac{1}{4}m}})}}}}}}} & (13)\end{matrix}$

For each frequency product of interest (F), the appropriate m, n pairscan be found which satisfy the correct frequency conditions in Equations12 and 13. Note, however, that the frequency products yielding F=kf (forinteger ‘k’s) are not generated.

Second Embodiment: Non-Harmonic DCO With XOR and Jitter Compensation #1

A block diagram illustrating a second embodiment of the local oscillatorgeneration mechanism of the present invention is shown in FIG. 11. Thecircuit, generally referenced 300, comprises a synthesizer 304, T/4delay 306, frequency divider 308, XOR gate 314, ±T/12 delay 318 andcontrol unit 320.

In operation, a reference signal f_(REF) 302 is input to a synthesizertuned to exactly ⅔ f_(RF). Alternatively, the 4/3 f_(RF) configurationwith a quadrature divider generating 90-degree spaced clocks could beused. In this case, the T/4 delay would not be needed. The digitaloutput of the synthesizer is input to a T/4 delay 306 and a divide bytwo circuit 308. The outputs of both blocks are XORed together via XORcircuit 314. The output of the XOR circuit is input to a programmable±T/12 delay 318. Since the absolute delay of block 318 does not changethe overall structure, a “negative delay” can be achieved using twopaths whose relative delay difference is 2*T/12=T/6.

The ±T/12 delay block is controlled by control unit (CU) 320 whichselects the delay that should be taken based on the X1 324 and X2 326input ports. The control unit logic may be implemented in any suitablemanner to yield the desired waveform. For example, the control unit maycomprise a state machine appropriately programmed (known to one skilledin the art) such that on rising edges of X1 the delay is set to +T/12,while on falling edges, the delay is set to −T/12. Thus, the controlunit determines which way the output LO clock 322 is pulled. Risingedges of X1, the output LO clock is pulled forward, while falling edgespull the output LO clock back.

A timing diagram illustrating the various time domain traces for thesecond embodiment local oscillator generation mechanism of the presentinvention of FIG. 11 is shown in FIG. 12. Trace 330 represents the X1signal 324 while trace 332 represents the X2 signal 326. The result ofthe XORing of the X1 and X2 signals is represented by trace 334. Thearrows in this trace indicate the direction of the delay required on theXOR signal 316 in order to create a perfect square wave clock (shown astrace 336). Arrows heading to the right indicate a positive delay whilearrows leading to the left indicate a negative delay, wherein negativedelays are implemented by manipulating the relative delay difference asdescribed supra.

Note that the relationship between 334 and 336 exhibits momentary“negative delays”, but it is well understood to one skilled in the artthat if trace 334 was moved forward by 2*T/12=T/6, then the relativedelays would be either 0 or T/12, thus establishing causality for thesystem. Please note that if the delays are perfectly T/12 then thegenerated signal has zero undesirable products.

Third Embodiment: Non-Harmonic DCO With XOR and Jitter Compensation #2

A block diagram illustrating a third embodiment of the local oscillatorgeneration mechanism of the present invention is shown in FIG. 13. Thecircuit, generally referenced 340, is a second implementation of thelocal oscillator generation scheme of FIG. 11. The circuit 340 comprisesa synthesizer 344, T/4 delay 348, frequency divider 350, −T/12 delaycircuit 353, T/12 delay circuit 354, multiplexer 358 and control unit(CU) 360.

In operation, a reference signal 342 is input to a synthesizer 344 tunedto exactly ⅔ f_(RF). The digital signal 346 output of the synthesizer isinput to both a T/4 delay circuit 348 as well as divide by two circuit350, which are operative to generate signals X1 362 and X2 364,respectively. Note that here too, as described before, the T/4 delaycircuit 348 is not needed if a quadrature generation of the 346 signalis available. Signal X1 undergoes delays of −T/12 via delay circuit 352and +T/12 via delay circuit 354. The outputs of the delay circuits 353,354 and signal X2 are input to a multiplexer 358 whose select controlinput is generated by the control unit 360, which may be implemented asa state machine or any other suitable processing or computing element.The inputs to the control unit comprise the signals X1 and X2. It isappreciated that one skilled in the electrical arts can program thecontrol unit such that the multiplexer outputs a perfect clock signal insimilar fashion to the circuit of FIG. 11.

Note that the implementations of both FIGS. 11 and 13 utilizeasynchronous delays that can be implemented in deep-submicron processesusing pre-calibrated inverter chains.

Note further that the pulling of edges of signal 334 in FIG. 12 in thetime domain is equivalent to reducing the unwanted harmonics in thefrequency domain. The non-perfect ±T/12 timing adjustments result innon-zero spurious energy of the harmonics. The amount of harmonicreduction is proportional to how close the timing delay is achieved.With a reasonable amount of inaccuracy, however, a substantial reductioncould be achieved. This method could be combined with the use of bandpass filtering, which in this embodiment would require less stringentfiltering specifications.

Fourth Embodiment: LO Generation Circuit #1

A block diagram illustrating a fourth embodiment of the local oscillatorgeneration mechanism of the present invention is shown in FIG. 14. Thecircuit, generally referenced 370, comprises a synthesizer 374,frequency dividers 376, digital logical mixing blocks 380, 382, weights386, 390, summers 392, 394 and band pass filters 400, 402.

In operation, a frequency reference signal f_(REF) 372 is input to thesynthesizer 374 timed to a rational multiplier of the RF frequencyf_(RF). This signal is divided down via frequency dividers circuit 376.Please note that circuit 376 typically comprises several dividers andits outputs may be the result of multiple, sometime cascaded, divisionoperations. The output of the frequency dividers is a plurality ofphases 378 at various division ratios of the divided signal and stageswithin the division. For example, considering a division ratio of four,the divider can be implemented as a cascade of two divide by twocircuits where the outputs are the in-phase and quadrature of the firstdivider, the in-phase and quadrature of a second divider operating onthe in-phase of the first divider and the in-phase and quadraturesignals of a second divider operating on the quadrature signal of thefirst divider.

The divided signals and phases 378 undergo processing by digital logicalmixing block 1 380 which is operative to generate a plurality ofcombination signals 384 (M in total). Note that digital logical mixingblock 1 may comprise either combinatory logic (represented by atruth-table), a finite state machine (FSM) or a combination thereof. Theplurality of signals 384 output of digital logical mixing 1 undergomultiplication by a set of weights w₀ . . . w_(M) 386 followed bysummation via adder 392 to yield in-phase signal 396.

Note that the circuit 370 comprises a semi-analog operation and can beimplemented in numerous ways, as is appreciated by one skilled in theelectrical arts. Examples of implementation of this circuit include (1)summation of current sources onto a load using binary or thermometryweighted CMOS transistors; and (2) using resistor or capacitor valueratios to sum voltages or currents.

A quadrature signal can be generated using optional block 404. Digitallogical mixing block 2 382 outputs a different plurality of combinationsignals 388 (L in total) which is multiplied by a different set ofweights W′₀ . . . W′_(L) 390 and summed via adder 394 to yieldquadrature signal 398.

Finally, the summed values output of adders 392, 394 are filtered viaBPF filters 400, 402 to yield the output LO_(I) (f_(LOI)) 406, LO_(Q)(f_(LOQ)) 408 signals, respectively. The summing operation effectivelycancels out or significantly attenuates some of the undesired productsto create a signal which is significantly easier to filter than thatobtained using conventional mixing. A key benefit of this fourthembodiment of the present invention is that by operating the localoscillator at a rational multiplier of the RF frequency, the undesirablesidebands are kept low which eases or completely obviates any requiredfiltering.

Fifth Embodiment: LO Generation Circuit #2

A block diagram illustrating a fifth embodiment of the local oscillatorgeneration mechanism of the present invention is shown in FIG. 15. Thisfifth embodiment is an example implementation of the LO generationcircuit (fourth embodiment) of FIG. 14. The circuit, generallyreferenced 410, comprises frequency dividers 417, digital logical mixing419 and weighting 421 blocks. The frequency dividers 417 block, coupledto synthesizer 412, comprises cascaded frequency dividers 414, 420, 426and inverters 416, 429. The digital logical mixing block 419 comprisesXOR gates 434, 438, 442. The weighting 421 block, coupled to band passfilter 454, comprises multipliers 446, 448, 450 and adder 452.

In operation, frequency reference signal f_(REF) 411 is input to thefrequency synthesizer 412 running at 4/3 f_(RF). The output of thesynthesizer is divided by two via divider circuit 414 which outputs aquadrature pair I 418 and Q 422. The in-phase signal I 418 is dividedagain by divider circuit 420 into in-phase signal II 430 and aquadrature signal IQ. The quadrature signal Q 422 undergoes division bytwo via block 426 to yield a quadrature set QI 432 and QQ 428. Signal I418 is also negated via inverter (i.e. not) circuit 416 to yield signal˜I 435. Similarly, signal QQ 428 is negated via inverter (i.e. not)circuit 429 to yield signal ˜QQ 431.

XOR circuit 434 is operative to XOR signals I with signal ˜QQ to yieldsignal 436. XOR circuit 438 is operative to XOR signals II and Q toyield signal 440. XOR circuit 442 is operative to XOR signals ˜I and QIto yield signal 444. Signals 436, 440, 444 are multiplied by constantweights of 5, 7, 5, respectively. The weighted output signals are summedvia adder 452. This summed signal undergoes filtering via BPF filtercircuit 454. Note that the weights may be applied, for example, usinganalog multipliers, DPA circuits, op amps or any other suitabletechnique. Further, the filter alone is not sufficient to filter out the⅓ f_(RF) signal, as greater than 90 dB attenuation is required for someapplications (e.g., Bluetooth in a cellular phone), which is verydifficult to achieve. The action of the weights and summer effectivelycancel the ⅓ f_(RF) component and amplifies the f_(RF) component.

To aid in illustrating the principles of operation of this fifthembodiment, a phasor diagram illustrating the relationship between theproducts generated in the LO generation circuit of FIG. 15 is shown inFIG. 16. The phasor diagram shows the three generated signals. Thevector arrows represent phasors of the generated signals in both thefundamental at f_(RF) as well as the first undesired product (i.e.sub-harmonic) at f_(RF)/3. Phasor 468 represents signal 436 at f_(RF)/3(¾π rotated product); phasor 470 represents signal 444 at f_(RF)/3;phasor 466 represents signal 440 at f_(RF)/3; phasor 460 represents the9/4π rotated fundamental; phasor 462 represents the f_(RF) component ofsignal 440; and phasor 472 represents the sum of phasors 468 and 470(i.e. the sum of ¾π and −¾π product rotations).

It is important to note that any phase difference ΔΘ between two signalsat f_(RF)/3 yields a phase difference of 3ΔΘ at f_(RF). The radius ofthe inner circle 471 represents the magnitude of the f_(RF)/3 componentswhile the radius of the outer circle 473 radius represents the magnitudeof the f_(RF) component. Without limiting generality, the phasors ofsignal 440 (i.e. X7 weight) are placed on the x axis. Hence phasor 466is the f_(RF)/3 component of signal 440 (i.e. the main signal), whilephasor 462 is the f_(RF) component thereof.

The two auxiliary signals 436 and 444 have f_(RF)/3 components rotatedby ¾π and −¾π (i.e. 468 and 470, respectively) with respect to the mainsignal. Therefore, their f_(RF) counterparts are rotated by 9/4π and −9/4π (phasors 460 and 464), respectively, with respect to the mainsignal component at f_(RF). Summing phasors 468 and 470, which have aπ/2 phase difference between them, yields a vector with a magnitude of√2 larger than each one and the main signal component at f_(RF)/3 466with an angle of π with respect to it. Hence, the main signal should bemultiplied by √2 (or each auxiliary signal by 1/√{square root over (2)})in order to achieve perfect cancellation at f_(RF)/3. Alternatively, themain signal is multiplied by 7 and each one of the auxiliary signals by5. Since 7/5≅√{square root over (2)} to about 1% of accuracy a veryreasonable cancellation is achieved.

The cancellation can be calculated as follows:

20 log 10(|5·√{square root over (2)}−7|)≅−23 dB   (14)

Using this rational approximation makes the implementation simpler dueto the ability to use thermometric weighted current sources or CMOStransistors. At the fundamental frequency f_(RF), the auxiliary signalcomponents add to the main signal component to create an even largercomponent. Since each one of the phasors 460 and 464 have a π/4 anglewith phasor 462 and they are equal in magnitude, their sum is collinearwith phasor 462 and has a magnitude of (7+5√{square root over (2)})=23dB larger than the original size of phasor 462. The net cancellation(increase in fundamental at f_(RF) combined with component attenuationat f_(RF)/3) is 23+23=46 dB. Adding this to the original 5 dB differencebetween the fundamental and the component at f_(RF)/3, we obtain a 51 dBtotal difference. Depending on the implementation, this may requireadditional light attenuation or may be sufficient and the filter 454(FIG. 15) can be replaced with a low pass filter, which is easier andless costly to implement.

A timing diagram illustrating the various time domain traces for thefifth embodiment local oscillator generation mechanism of the presentinvention shown in FIG. 15 is shown in FIG. 17. The timing diagram showsthe time domain traces for the various signals in the circuit 410 ofFIG. 15. Traces 474, 476, 478, 480, 482, 484 represent signals I, Q, II,QI, IQ, QQ, respectively. Trace 486 shows the main signal at weight 448,trace 488 shows the auxiliary signal at weight 446 and trace 490 showsthe auxiliary signal at weight 450. Finally, trace 492 shows the sum ofall weighted contributions (i.e. output of adder 452), which afterfiltering is the desired f_(LO) output clock.

A graph illustrating the spectrum magnitude plot of the output of thecircuit of FIG. 15 is shown in FIG. 18. In particular, the spectrummagnitude plot shows the power spectral magnitude of trace 492.Component 500 at f_(RF)/3 has roughly a 50 dB attenuation with respectto the fundamental (i.e. desired) component 502 at f_(RF). The nextundesired component is at 5/3 f_(RF) and is relatively easy to filtersince it is almost an entire octave away from the fundamental component.There are additional undesirable components 506, 508, 510 at 7/3 f_(RF),3 f_(RF), 11/3 f_(RF), respectively. Thus, since the first undesiredcomponent 500 has an approximate 50 dB attenuation, the relativelyexpense band pass filter 454 (FIG. 15) can be replaced with a lower costlow pass filter.

Sixth Embodiment: LO Generation Circuit with Pulse Generation #1

A block diagram illustrating a sixth embodiment of the local oscillatorgeneration mechanism of the present invention is shown in FIG. 19. Thecircuit, generally referenced 520, comprises a frequency synthesizer524, frequency dividers 528, 548, pulse generator 532, selector block536, control unit 544 and optional filter 540.

In operation, a frequency reference signal f_(REF) 522 is input to thefrequency synthesizer 524 operating at a rational multiplier of the RFfrequency f_(RF). The synthesizer generates a clock signal 526 at L/Nf_(RF), where L and N are integer numbers. The clock signal 526 is thendivided by a factor of Q via divider circuit 528 to form exactly 2Qphases 530 of the clock at a frequency of L/(N*Q)f_(RF). Each phase thenundergoes division by L using divider circuits 548. The 2Q phase signals530 are also input to pulse generator circuit(s) 532 which may comprisedigital combinatory logic circuitry or asynchronous circuitry such as amono-stable. The output of the pulse generator comprises a plurality ofpulse signals 534 which are input to a selector block 536. The selectorblock functions to select which signal out of the plurality of pulsesignals 534 to output as signal 538 at any point in time. The selectorcircuit may be implemented in any suitable manner such as a multiplexer,combinatory logic or a finite state machine (FSM).

A control unit (CU) 544 functions to receive both the output of theselector 538 as well as the output of dividers 548. Based on the inputs,the control unit outputs a select signal 546 which indicates to theselector 536 which of the pulses 534 to output at any given moment. Theresultant signal 538 is the local oscillator clock signal which isgenerated in TDM fashion from the plurality of pulses 534. An optionalfilter 540 eliminates any undesired frequency spurs. Note that in thecase of N=2, there are sufficient grid points to generate a fullyperiodic signal without any frequency spurs. Implementationimperfections, however, may generate spurious tones which may requirefiltering to limit the spurious spectrum of the output signal f_(LO).

Seventh Embodiment: LO Generation Circuit with Pulse Generation #2

A block diagram illustrating a seventh embodiment of the localoscillator generation mechanism of the present invention is shown inFIG. 20. The circuit, generally referenced 550, comprises frequencysynthesizer 552, frequency dividers 556, 586, 588, 590, 592, gates 562,566, 570, 574, 602, 604, 606, 608, 610 and optional filter 614.

In operation, a frequency reference signal f_(REF) 551 is input to thefrequency synthesizer 552 tuned to exactly 3/2 f_(RF). The output 554 ofthe synthesizer is input to a divide by two circuit 556 which producesfour phases of the input signal at an exact frequency of ¾ f_(RF). Thefour phases are denoted by their quadrature names and inverses, namelysignal I 578, signal Q 580, signal ˜I (i.e. not I) 582 and signal ˜Q(i.e. not Q) 584. These four signals are input to the pulse generatorcircuit 560 which comprises four AND gates 562, 566, 570, 574. The fourAND gates perform a logical AND operation between each possible pair ofcontiguous phases. In particular, AND gate 562 performs its operationbetween the I and Q signals to generate I&Q (i.e. I and Q) signal 564.AND gate 566 performs its operation between the I and ˜Q signals togenerate I&˜Q (I AND NOT(Q)) signal 568. AND gate 570 performs itsoperation between the ˜I and ˜Q signals to generate ˜I&˜Q (NOT(I) ANDNOT(Q)) signal 572. AND gate 574 performs its operation between ˜I and Qsignals to generate ˜I&Q (NOT(I) and Q) signal 576. The four pulseoutput signals 564, 568, 572, 576 are input to the combinedselector/control unit block 616.

The four phase signals output of the divide by two circuit 556 alsoundergo division by three. Divide by three circuit 586 divides the ˜Qsignal 584 to generate ˜Q/3 signal 594 (NOT(Q) divided by three). Divideby three circuit 588 divides the ˜I signal 582 to generate ˜I/3 signal596 (NOT(I) divided by three). Divide by three circuit 590 divides the Qsignal 580 to produce Q/3 signal 598 (Q divided by three). Divide bythree circuit 592 divides the I signal 578 to generate I/3 signal 600 (Idivided by three).

Combined selector and control unit 616 comprises four AND gates 602,604, 606, 608, which AND the four divide by three output signals withtheir respective pulse signals. The respective results are wire-ORedtogether by OR circuit 610. The effective operation of theselector/control unit is to use the divide by three outputs 594, 596,598, 600 as “one-hot” controls to select which pulse out of the fourpulses (564, 568, 572, 576 ) will be output by the block. Note that indigital circuits, the term one-hot refers to a group of bits among whichthe legal combinations of values are only those with a single high (“1”)bit and all the others low (“0”). Note also that this circuit preferablyhas an output with no sub-harmonics (lowest spectral tone being atf_(RF)), which permits much simpler filtering. An optional filter 614can be used to attenuate any unwanted frequency spurs.

A timing diagram illustrating the various time domain traces for thesixth embodiment local oscillator generation mechanism of the presentinvention of FIG. 20 is shown in FIG. 21. Trace 620 represents theoutput ˜Q/3 594, trace 622 represents the output ˜I/3 596, trace 624represents the output Q/3 598 and trace 626 represents the output I/3600. As can be seen from the timing diagram, the outputs of the dividersprovide wide signals which can be used to gate the pulses in order toproduce a perfect pulse train. Although this is not a perfect “one-hot”scheme where only one of these wide pulses can be active at any time,the situation where this might impede with the normal circuit operationis limited to the case of a pulse occurring in the overlap of two of thedivider signals which is prevented by this circuit. Traces 628 and 630represent the Q and I outputs, respectively. Trace 632 shows the outputof AND gate 608. As can be seen, the narrow pulses generated by thepulse generation circuit are gated by the wide gate signals (signal 626I/3 in this case) to produce one of the pulse phases ORed together toproduce the f_(LO) output clock signal 612 (FIG. 20) represented bytrace 634.

A graph illustrating the spectrum magnitude plot of the output of thecircuit of FIG. 20 is shown in FIG. 22. The spectrum magnitude plot isof the FIG. 12 b shows a spectral plot of the f_(LO) output clock signal612 (trace 634). As can be seen, the lowest frequency tone 640 isproduced at f_(RF). Undesired tones 642 and 644 appear at the evenharmonics 2 f_(RF) and 4 f_(RF), respectively.

Eighth Embodiment: LO Generation Circuit with Pulse Generation #3

A block diagram illustrating an eighth embodiment of the localoscillator generation mechanism of the present invention is shown inFIG. 23. The circuit, generally referenced 650, is a second exampleembodiment of the sixth embodiment of FIG. 19. The circuit 650 comprisesfrequency synthesizer 652, frequency divider 654, multiplexer 664,counter 668 and optional filter 672.

In operation, a frequency reference signal f_(REF) 651 is input to thefrequency synthesizer 652 running at 3/2 f_(RF). The signal frequencyoutput of the synthesizer is divided by two via divider circuit 654which has four phase outputs, namely, the quadrature pair I and Q (656and 658, respectively) and their inverses ˜I and ˜Q (660 and 662,respectively). The four phases are input to a multiplexer 664 whichfunctions to output the desired local oscillator signal. The controlunit in this embodiment which controls the multiplexer selectioncomprises a modulo-4 counter 668. The counter is clocked by the localoscillator output signal 670 and the output 666 is input to theselecting input of the multiplexer. In this embodiment, the selectorcircuit is implemented as the multiplexer 664 while the control unit isimplemented as a modulo-4 counter 668. An optional filter 672 removesany unwanted frequency spurs.

It is noted that, in an alternative embodiment, the selecting input 666is advantageously driven by one of the four phases of the output ofdivider 654. Driving a multiplexer selecting input by a signal that doesnot depend on the multiplexer output can be considered beneficial as isprovides for more reliable operation.

A timing diagram illustrating the various time domain traces for theeighth embodiment local oscillator generation mechanism of the presentinvention of FIG. 23 is shown in FIG. 24. The timing diagram shows thevarious time domain traces for the signals of the circuit 650 of FIG.23. Traces 680, 682, 684 and 686 represent the four phases (i.e. ˜Q, ˜I,Q and I), respectively. The thick lines in the traces represent theportions which are multiplexed to the output via multiplexer 664. Trace688 represents the output of the counter 668. Trace 689 represents theoutput waveform f_(LO) 674. As can be seen, notwithstanding a duty cycleaberration, the output waveform is a perfect signal at f_(RF).

A graph illustrating the spectrum magnitude plot of the output of thecircuit of FIG. 23 is shown in FIG. 25. It is evident from the plot thatthe circuit does not generate a component at f_(RF)/3 and the largestfrequency component 690 is at f_(RF). In addition, even harmonics existas undesired signals 692, 694 at 2 f_(RF), 3 f_(RF), etc. It is notedthat the output local oscillator clock signal does not requirefiltering. Lower frequency components, however, may be created by timingmismatches at the multiplexer input. These unwanted frequency spurs canbe minimized using careful analog design and layout techniques.

Ninth Embodiment: Non-Integer Local Oscillator Using Spectral Replicas

The ninth embodiment is described in the context of an example wirelesslink using non-integer LO incorporating a Cartesian DPA. A more detaileddescription of the operation of the DPA in the Cartesian transmitter canbe found in U.S. Patent Publication No. 2006/0038710A1, cited supra.

The wireless link device may comprise any suitable device such as amultimedia player, mobile device, cellular phone, PDA, etc. Forillustration purposes, the wireless link comprises a WLAN embedded in amobile transmission and reception link. Note that this example is notintended to limit the scope of the invention as the Cartesian basedreplicas non-integer LO mechanism of the present invention can beimplemented in a wide variety of communication devices.

The ninth embodiment utilizes spectral replicas generated whenincorporating a zero order hold effect of the Digital Power Amplifier(DPA) during the modulation of a wideband signal. The sampling rate ofthe DPA is specifically configured such that one of the replicas fallsdirectly in the desired in-band frequency. All other replicas arefiltered using analog or digital filtering. The other replicas are setto fall into specific frequency bands that do not cause any interferenceto other radios. This allows the requirements of the analog filtering atthe last stage to be significantly relaxed and thus simpler and lesscostly to implement.

A block diagram illustrating a ninth embodiment of the local oscillatorgeneration mechanism of the present invention incorporating theCartesian based non-integer local oscillator is shown in FIG. 26. Theexample transmitter circuit, generally referenced 700, comprisesinterpolators/upsamplers 702, 704, quadrature mixer 706, localoscillator 708, DPA circuits 710, 712, adder 714, band pass filter 716and amplifier 718.

The transmitter 700 incorporates the Cartesian based dual DPAnon-integer local oscillator of the present invention. In operation, theI and Q complex input baseband signal S_(BB)(n) is upsampled andinterpolated via blocks 702 and 704, respectively. The output of theinterpolators are then upconverted in the digital domain using complexmultiplier 706 resulting in a signal I_(IF)(n)+jQ_(IF)(n) centered atIF. The IF frequency is adjusted to be half the LO's frequency so as tofit in the upconversion of the next stage.

The LO 708 is tuned to operate at a frequency which is a non integerratio N/M of the LO to RF. Note that in the case of a Bluetooth or WLANsignal this ratio could be set to 3/2 division of the target RFfrequency f_(RF). The IF frequency is set to be half of the LO frequencyso that the sampling rate of the last digital stage is equal to the LOfrequency. The digital IF signal is then converted to the analog domainusing two DPA circuits 710 and 712 for I and Q branches, respectively.The DPA circuits function to create two analog signals for the in-phaseI and quadrature Q signals wherein the resulting signals includemultiple replicas of the signals at f_(IF), f_(IF)+f_(LO), f_(IF)+2f_(LO), etc., due to the ZOH nature of the DPA circuits.

The resultant I and Q analog signals are then combined via adder 714(e.g., voltage or current combiner). The output of the adder is thenfiltered using BPF 716 to extract the desired replica. The frequency ofthe replica is selected so that it does not fall in any cellular band.Attenuation is required only if the level of the replicas is above anyrequirement or standard (e.g., FCC, etc.). The filtered signal may beamplified by a power amplifier (PA) 718 that may be embedded on or offthe radio integrated circuit chip.

A simplified block diagram illustrating the DPA of the local oscillatorgeneration circuit of FIG. 26 in more detail is shown in FIG. 27. TheDPA circuit, generally referenced 720, comprises a plurality of gates722 and transistors 724, and an RF inductor portion of the load 726. Inoperation, the clock signal is gated with a control word (inputs D₁through D_(N)). The value of the control word at any instant in timedetermines the amplitude of the signal output of the DPA. The clocksignal (i.e. LO output) input to the DPA also functions as its samplingfrequency. Therefore, the spectrum at the output of the complexmultiplier is repeated every sampling frequency f_(S). Thus, an analogmixer is not required for further upconversion since the first replicaof the DPA output can be used instead. The replicas generated by the ZOHeffect of the DPA are repeated every sampling frequency (i.e. the LOfrequency). Since the complex IF signal is located at the f_(LO)/2 thanthe first replica will be located at f_(LO)+f_(LO)/2.

As an example, consider a Bluetooth transmission. In this Bluetoothexample, the RF frequency f_(RF) is tuned to 2402 MHz (i.e. the firstBluetooth channel). The local oscillator frequency is therefore tuned tof_(LO)=f_(RF)/3=1601.33 MHz. In this case, the DPA also creates a verystrong replica (only 13 dB less than the “main replica”) positioned atf_(RF)=f_(LO)+f_(IF)=f_(LO)+f_(LO)/2=( 3/2)*f_(LO)=( 3/2)*1601.33=2402MHz.

A graph illustrating simulation results of the spectrum at the output ofthe transmitter employing the Cartesian based non-integer localoscillator of FIG. 26 is shown in FIG. 28. Note that the 2402 MHz peakshown is obtained as a result of filtering the first replica.

The ninth embodiment thus provides an efficient method to implement thelocal oscillator and to generate the required clock signal. The methoduses a complex multiplier intended to shift the zero baseband signalsuch that it is centered on f_(LO)/2 (e.g., 1601.33/2=800.6 MHz).Subsequent processing by the two DPA circuits generates outputs whichare easily combined using a voltage or current combiner. The two DPAcircuits and combiner could further be simplified by connecting thedrain junction of each of the DPAs to the same inductor used to pump thecurrent during the transitions of the DPA thereby reducing thecomplexity of the combiner.

It is intended that the appended claims cover all such features andadvantages of the invention that fall within the spirit and scope of thepresent invention. As numerous modifications and changes will readilyoccur to those skilled in the art, it is intended that the invention notbe limited to the limited number of embodiments described herein.Accordingly, it will be appreciated that all suitable variations,modifications and equivalents may be resorted to, falling within thespirit and scope of the present invention.

1. An apparatus for generating a local oscillator signal having anoutput frequency, comprising: an oscillator circuit operative togenerate a first signal, said first signal having a frequencysubstantially equal to a rational multiplier L/N of said outputfrequency; a frequency divide by Q coupled to receive said first signaland operative to generate 2Q second signal phases at a frequencysubstantially equal to a rational multiplier L/(N*Q) of said outputfrequency; a pulse generator operative to generate a plurality of pulsesignals from said 2Q second signal phases; a frequency divider by Lcoupled to receive said 2Q second signal phases and operative togenerate a plurality of third signals; a selector operative to select,using time division multiplexing, one of said plurality of pulse signalsas an output signal in accordance with a select control signal, saidoutput signal having a frequency substantially equal to said outputfrequency; and control means for generating said select control signalas a function of said plurality of third signals and said output signal.2. The apparatus according to claim 1, wherein said first frequencysubstantially equals L/N= 3/2 of said output frequency and Q is equal totwo.
 3. The apparatus according to claim 1, further comprising a filtercoupled to receive said output signal and operative to remove unwantedproducts therefrom.
 4. The apparatus according to claim 1, wherein saidpulse generator comprises 2Q AND gates, each gate coupled to a pair ofadjacent second signal phases.
 5. The apparatus according to claim 1,wherein said selector and control means comprise: means for gating eachone of said third signals with a corresponding one of said pulse signalsto generate a plurality of gated signals; and means for ORing saidplurality of gated signals together to generate said output signalthereby.
 6. A method of generating a local oscillator signal having anoutput frequency, said method comprising the steps of: generating afirst signal at a first frequency, said first signal having a frequencysubstantially equal to a rational multiplier L/N of said outputfrequency; dividing said first signal by Q to generate 2Q second signalphases at a frequency substantially equal to a rational multiplierL/(N*Q) of said output frequency; generating a plurality of pulsesignals from said 2Q second signal phases; dividing each of said 2Qsecond signal phases by L to generate a plurality of third signals; andselecting, using time division multiplexing, one of said plurality ofpulse signals as an output signal having a frequency substantially equalto said output frequency, wherein said selection determined as afunction of said plurality of third signals and said output signal. 7.The method according to claim 6, wherein said first frequencysubstantially equals L/N= 3/2 of said output frequency and Q is equal totwo.
 8. The method according to claim 6, further comprising the step offiltering said output signal to remove unwanted products therefrom. 9.The method according to claim 6, wherein said plurality of pulse signalsare generated by gating pairs of adjacent second signal phases.
 10. Themethod according to claim 6, wherein said step of selecting comprisesthe steps of: gating each one of said third signals with a correspondingone of said pulse signals to generate a plurality of gated signals; andORing said plurality of gated signals together to generate said outputsignal thereby.
 11. An apparatus for generating a local oscillatorsignal having an output frequency, comprising: an oscillator circuitoperative to generate a first signal, said first signal having afrequency substantially equal to a rational multiplier L/N of saidoutput frequency; a frequency divider by Q coupled to receive said firstsignal and operative to generate 2Q second signal phases at a frequencysubstantially equal to a rational multiplier L/(N*Q) of said outputfrequency; a multiplexer coupled to receive said 2Q second signal phasesand operative to output one of said 2Q second signal phases as an outputsignal in accordance with a select control input; and a modulo-2Qcounter operative to generate an output coupled to said select controlinput, wherein the output of said counter causes said multiplexer tosequentially cycle through said 2Q second signal phases such that saidoutput signal substantially resembles a desired output clock signal. 12.The apparatus according to claim 11, wherein said first frequencysubstantially equals L/N= 3/2 of said output frequency and Q is equal totwo.
 13. The apparatus according to claim 11, further comprising afilter coupled to receive said output signal and operative to removeunwanted products therefrom.
 14. An apparatus for generating a localoscillator signal having an output frequency, comprising: an oscillatorcircuit operative to generate a quadrature clock of four substantiallyequally spaced phases, said quadrature clock having a frequencysubstantially equal to a rational multiplier ¾ of said output frequency;a multiplexer coupled to receive said quadrature clock and operative tooutput one of said four phases as an output signal in accordance with aselect control input; and a modulo-4 counter operative to generate anoutput coupled to said select control input, wherein the output of saidcounter causes said multiplexer to sequentially cycle through said fourphases of said quadrature clock.
 15. The apparatus according to claim14, further comprising a filter coupled to receive said output signaland operative to remove unwanted products therefrom.
 16. A radio,comprising: a transmitter coupled to an antenna, said transmittercomprising a local oscillator having an output frequency, said localoscillator comprising: an oscillator circuit operative to generate afirst signal, said first signal having a frequency substantially equalto a rational multiplier L/N of said output frequency; a frequencydivider by Q coupled to receive said first signal and operative togenerate 2Q second signal phases at a frequency substantially equal to arational multiplier L/(N*Q) of said output frequency; a pulse generatoroperative to generate a plurality of pulse signals from said 2Q secondsignal phases; a frequency divide by L coupled to receive said 2Q secondsignal phases and operative to generate a plurality of third signals; aselector operative to select, using time division multiplexing, one ofsaid plurality of pulse signals as an output signal in accordance with aselect control signal, said output signal having a frequencysubstantially equal to said output frequency; control means forgenerating said select control signal as a function of said plurality ofthird signals and said output signal; a receiver coupled to saidantenna; and a baseband processor coupled to said transmitter and saidreceiver.
 17. The radio according to claim 15, wherein said firstfrequency substantially equals L/N= 3/2 of said output frequency and Qis equal to two.
 18. The radio according to claim 16, further comprisinga filter coupled to receive said output signal and operative to removeunwanted products therefrom.
 19. The radio according to claim 16,wherein said pulse generator comprises 2Q AND gates, each gate coupledto a pair of adjacent second signal phases.
 20. The radio according toclaim 16, wherein said selector and control means comprise: means forgating each one of said third signals with a corresponding one of saidpulse signals to generate a plurality of gated signals; and means forORing said plurality of gated signals together to generate said outputsignal thereby.
 21. A radio, comprising: a transmitter coupled to anantenna, said transmitter comprising a local oscillator having an outputfrequency, said local oscillator comprising: an oscillator circuitoperative to generate a first signal, said first signal having afrequency substantially equal to a rational multiplier L/N of saidoutput frequency; a frequency divide by Q coupled to receive said firstsignal and operative to generate 2Q second signal phases at a frequencysubstantially equal to a rational multiplier L/(N*Q) of said outputfrequency; a multiplexer coupled to receive said 2Q second signal phasesand operative to output one of said 2Q second signal phases as an outputsignal in accordance with a select control input; a modulo-2Q counteroperative to generate an output coupled to said select control input,wherein the output of said counter causes said multiplexer tosequentially cycle through said 2Q second signal phases such that saidoutput signal substantially resembles a desired output clock signal; areceiver coupled to said antenna; and a baseband processor coupled tosaid transmitter and said receiver.
 22. The radio according to claim 21,wherein said first frequency substantially equals L/N= 3/2 of saidoutput frequency and Q is equal to two.
 23. The radio according to claim21, further comprising a filter coupled to receive said output signaland operative to remove unwanted products therefrom.